Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Ying Chen, Yupeng Liao, Lisha Yuan, Hui Liu, Seong Dae Yun, Nadim Joni Shah, Zhong Chen, Jianhui Zhong Single-shot spatiotemporally encoded (SPEN) MRI is a novel fast imaging method capable of retaining the time efficiency of single-shot echo planar imaging (EPI) but with distortion artifacts significantly reduced. Akin to EPI, the phase inconsistencies between mismatched even and odd echoes also result in the so-called Nyquist ghosts. However, the characteristic of the SPEN signals provides the possibility of obtaining ghost-free images directly from even and odd echoes respectively, without acquiring additional reference scans. In this paper, a theoretical analysis of the Nyquist ghosts manifested in single-shot SPEN MRI is presented, a one-dimensional correction scheme is put forward capable of maintaining definition of image features without blurring when the phase inconsistency along SPEN encoding direction is negligible, and a technique is introduced for convenient and robust correction of data from multi-channel receiver coils. The effectiveness of the proposed processing pipeline is validated by a series of experiments conducted on simulation data, in vivo rats and healthy human brains. The robustness of the method is further verified by implementing distortion correction on ghost corrected data. Graphical abstract

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Panayiotis Mavroidis, Eleonora Giankou, Aleksandra Tsikrika, Eftichia Kapsalaki, Vasiliki Chatzigeorgiou, Georgios Batsikas, Georgios Zaimis, Spiros Kostopoulos, Dimitrios Glotsos, Konstantinos Ninos, Vasilios Georgountzos, Dionisios Kavouras, Eleftherios Lavdas Introduction Although T1 weighted spin echo (T1W SE) images are widely used to study anatomical details and pathologic abnormalities of the brain, its role in delineation of lesions and reduction of artifacts has not been thoroughly investigated. BLADE is a fairly new technique that has been reported to reduce motion artifacts and improve image quality. Objective The primary objective of this study is to compare the quality of T1-weighted fluid attenuated inversion recovery (FLAIR) images with BLADE technique (T1W FLAIR BLADE) and the quality of T1W SE images in the MR imaging of the brain. The goal is to highlight the advantages of the two sequences as well as which one can better reduce flow and motion artifacts so that the imaging of the lesions will not be impaired. Materials and methods Brain examinations with T1W FLAIR BLADE and T1W SE sequences were performed on 48 patients using a 1.5 T scanner. These techniques were evaluated by two radiologists based on: a) a qualitative analysis i.e. overall image quality, presence of artifacts, CSF nulling; and b) a quantitative analysis of signal-to-noise ratios (SNR), contrast-to-noise ratios (CNR) and Relative Contrast. The statistical analysis was performed using the Kruskal-Wallis non-parametric system. Results In the qualitative analysis, BLADE sequences had a higher scoring than the conventional sequences in all the cases. The overall image quality was better on T1W FLAIR BLADE. Motion and flow-related artifacts were lower in T1W FLAIR BLADE. Regarding the SNR measurements, T1W SE appeared to have higher values in the majority of cases, whilst T1W-FLAIR BLADE had higher values in the CNR and Relative Contrast measurements. Conclusion T1W FLAIR BLADE sequence appears to be superior to T1W SE in overall image quality and reduction of motion and flow-pulsation artifacts as well as in nulling CSF and has been preferred by the clinicians. T1W FLAIR BLADE may be an alternative approach in brain MRI imaging.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Gabriela Trifan, Ramtilak Gattu, Ewart Mark Haacke, Zhifeng Kou, Randall R. Benson Traumatic brain injury (TBI) is a widespread cause of neurologic disability, with > 70% of cases being mild in severity. Magnetic resonance imaging provides objective biomarkers in the diagnosis of brain injury by detecting brain lesions resulting from trauma. This paper reports on the detection rates of presumed trauma-related pathology using fluid-attenuated inversion recovery (FLAIR) and susceptibility-weighted imaging (SWI) in TBI patients with chronic, persistent symptoms. Methods: 180 subjects with persistent neurobehavioral symptoms following head trauma referred by personal injury attorneys and 94 asymptomatic, age-matched volunteers were included in the study. 83% of TBI subjects were classified as mild. Results: TBI subjects had a significantly greater number of lesions detected by FLAIR than controls (42% vs. 22%) and more lesions detected by SWI than controls (28% vs. 3%). To reduce the confounding effects of aging, we examined mild TBI subjects 〈 45 years of age, which reduced the rate of lesions detected by FLAIR (26% vs. 2%) and SWI (15% vs. 0%). This younger group, which contained few age-related lesions, also demonstrated that subcortical lesions on FLAIR are more specific for TBI than deeper lesions. Conclusions: While the presence of litigation in mild TBI cases with incomplete recovery has been associated with greater expression of symptomatology and, by extension, poorer outcomes, this study shows that mild TBI patients in litigation with chronic, persistent symptoms may have associated brain injury underlying their symptoms detectable by MRI biomarkers.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Ningzhi Li, Shizhe Li, Jun Shen Purpose Over the past decade, many techniques have been developed to reduce radiofrequency (RF) power deposition associated with proton decoupling in in vivo Carbon-13 ( 13 C) magnetic resonance spectroscopy (MRS). In this work we propose a new strategy that uses data under-sampling to achieve reduction in RF power deposition. Materials and methods Essentially, proton decoupling is required only during randomly selected segments of data acquisition. By taking advantage of the sparse spectral pattern of the carboxylic/amide region of in vivo 13 C spectra of brain, we developed an iterative algorithm to reconstruct spectra from randomly under-sampled data. Fully sampled data were used as references. Reconstructed spectra were compared with the fully sampled references and evaluated using residuals and relative signal intensity errors. Results Numerical simulations and in vivo experiments at 7 Tesla demonstrated that this novel decoupling and data processing strategy can effectively reduce decoupling power deposition by greater than 30%. Conclusion This study proposes and evaluates a novel approach to acquire 13 C data with reduced proton decoupling power deposition and reconstruct in vivo 13 C spectra of carboxylic/amide metabolite signals using randomly under-sampled data. Because proton decoupling is not needed over a significant portion of data acquisition, this novel approach can effectively reduce the required decoupling power and thus SAR. It opens the possibility of performing in vivo 13 C experiments of human brain at very high magnetic fields.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Sandra M. Meyers, Shannon H. Kolind, Alex L. MacKay Purpose This work demonstrates the in vivo application of a T 2 relaxation based total water content (TWC) measurement technique at 3 T in healthy human brain, and evaluates accuracy using simulations that model brain tissue. The benefit of using T 2 relaxation is that it provides simultaneous measurements of myelin water fraction, which correlates to myelin content. Methods T 2 relaxation data was collected from 10 healthy human subjects with a gradient and spin echo (GRASE) sequence, along with inversion recovery for T 1 mapping. Voxel-wise T 2 distributions were calculated by fitting the T 2 relaxation data with a non-negative least squares algorithm incorporating B 1 + inhomogeneity corrections. TWC was the sum of the signals in the T 2 distribution, corrected for T 1 relaxation and receiver coil inhomogeneity, relative to either an external water standard or cerebrospinal fluid (CSF). Simulations were performed to determine theoretical errors in TWC. Results TWC values measured in healthy human brain relative to both external and CSF standards agreed with literature values. Simulations demonstrated that TWC could be measured to within 3–4% accuracy. Conclusion In vivo TWC measurement using T 2 relaxation at 3 T works well and provides a valuable tool for studying neurological diseases with both myelin and water changes.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Ken Sakaie, Mark Lowe Purpose To quantify and retrospectively correct for systematic differences in diffusion tensor imaging (DTI) measurements due to differences in coil combination mode. Background Multi-channel coils are now standard among MRI systems. There are several options for combining signal from multiple coils during image reconstruction, including sum-of-squares (SOS) and adaptive combine (AC). This contribution examines the bias between SOS- and AC-derived measures of tissue microstructure and a strategy for limiting that bias. Methods Five healthy subjects were scanned under an institutional review board-approved protocol. Each set of raw image data was reconstructed twice—once with SOS and once with AC. The diffusion tensor was calculated from SOS- and AC-derived data by two algorithms—standard log-linear least squares and an approach that accounts for the impact of coil combination on signal statistics. Systematic differences between SOS and AC in terms of tissue microstructure (axial diffusivity, radial diffusivity, mean diffusivity and fractional anisotropy) were evaluated on a voxel-by-voxel basis. Results SOS-based tissue microstructure values are systematically lower than AC-based measures throughout the brain in each subject when using the standard tensor calculation method. The difference between SOS and AC can be virtually eliminated by taking into account the signal statistics associated with coil combination. Conclusions The impact of coil combination mode on diffusion tensor-based measures of tissue microstructure is statistically significant but can be corrected retrospectively. The ability to do so is expected to facilitate pooling of data among imaging protocols.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Junzhong Xu, Ke Li, R. Adam Smith, John C. Waterton, Ping Zhao, Zhaohua Ding, Mark D. Does, H. Charles Manning, John C. Gore Background Diffusion-weighted MRI (DWI) signal attenuation is often not mono-exponential (i.e. non-Gaussian diffusion) with stronger diffusion weighting. Several non-Gaussian diffusion models have been developed and may provide new information or higher sensitivity compared with the conventional apparent diffusion coefficient (ADC) method. However the relative merits of these models to detect tumor therapeutic response is not fully clear. Methods Conventional ADC, and three widely-used non-Gaussian models, (bi-exponential, stretched exponential, and statistical model), were implemented and compared for assessing SW620 human colon cancer xenografts responding to barasertib, an agent known to induce apoptosis via polyploidy. Bayesian Information Criterion (BIC) was used for model selection among all three non-Gaussian models. Results All of tumor volume, histology, conventional ADC, and three non-Gaussian DWI models could show significant differences between control and treatment groups after four days of treatment. However, only the non-Gaussian models detected significant changes after two days of treatment. For any treatment or control group, over 65.7% of tumor voxels indicate the bi-exponential model is strongly or very strongly preferred. Conclusion Non-Gaussian DWI model-derived biomarkers are capable of detecting tumor earlier chemotherapeutic response of tumors compared with conventional ADC and tumor volume. The bi-exponential model provides better fitting compared with statistical and stretched exponential models for the tumor and treatment models used in the current work.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Xiao Wang, Xiao-Hong Zhu, Yi Zhang, Afshin A. Divani, Amanda J. Murphy, Wei Chen The saturation-recovery (SR)-T 1 MRI method for quantitatively imaging cerebral blood flow (CBF) change (ΔCBF) concurrently with the blood oxygenation level dependence (BOLD) alteration has been recently developed and validated by simultaneous measurement of relative CBF change using laser Doppler flowmetry (LDF) in rats at 9.4T. In this study, ΔCBF induced by mildly transient hypercapnia and measured by the SR-T 1 MRI method was rigorously compared with an established perfusion MRI method—continuous arterial spin labeling (CASL) approach in normal and preclinical middle cerebral artery occlusion (MCAo) rat models. The results show an excellent agreement between ΔCBF values measured with these two imaging methods. Moreover, the intrinsic longitudinal relaxation rate (R 1 int ) was experimentally determined in vivo in normal rat brains at 9.4T by comparing two independent measures of the apparent longitudinal relaxation rate (R 1 app ) and CBF measured by the CSAL approach across a wide range of perfusion. In turn, the R 1 int constant can be employed to calculate the CBF value based on the R 1 app measurement in healthy brain. This comparison study validates the fundamental relationship for linking brain tissue water R 1 app and cerebral perfusion, demonstrates the feasibility of imaging and quantifying both CBF and its change using the SR-T 1 MRI method in vivo.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Yu Liu, Ying Teng, Lanlan Jiang, Jiafei Zhao, Yi Zhang, Dayong Wang, Yongchen Song It is of great importance to study the CO 2 -oil two-phase flow characteristic and displacement front behavior in porous media, for understanding the mechanisms of CO 2 enhanced oil recovery. In this work, we carried out near miscible CO 2 flooding experiments in decane saturated synthetic sandstone cores to investigate the displacement front characteristic by using magnetic resonance imaging technique. Experiments were done in three consolidated sandstone cores with the permeabilities ranging from 80 to 450 mD. The oil saturation maps and the overall oil saturation during CO 2 injections were obtained from the intensity of magnetic resonance imaging. Finally the parameters of the piston-like displacement fronts, including the front velocity and the front geometry factor (the length to width ratio) were analyzed. Experimental results showed that the near miscible vertical upward displacement is instable above the minimum miscible pressure in the synthetic sandstone cores. However, low permeability can restrain the instability to some extent.

Description: Publication date: April 2017 Source: Magnetic Resonance Imaging, Volume 37 Author(s): Radim Korinek, Karel Bartusek, Zenon Starcuk A number of ‘Dixon’ techniques based on fast spin echo (FSE) sequence have been proposed and successfully used in many branches of medicine. Some require only one scan, but most of them need multiple scans and long scan times. This article describes a new fast triple-spin-echo Dixon (FTSED) technique suitable for ultra-high field MRI, in which three specific time shifts are introduced in the echo train; thus, three images with defined water-fat phase-differences (0, π, 2π) are encoded in the phase of the acquired images without extreme restrictions upon the echo duration. The water and fat images are then calculated by iterative least-squares estimation method. The sequence was successfully implemented at a 9.4 T ultra-high field MRI system and tested on a phantom and a rat.